1. Field of the Invention
The invention relates to an ultrasonic transducer as an important part of an ultrasonic flow meter, with a transducer housing and a transducer element, the transducer housing having an ultrasound window, a housing tube and a housing flange, and there being a transducer element either on the end of the housing tube facing the medium whose flow rate is to be measured or on the end of the housing tube facing away from the medium whose flow rate is to be measured, and the ultrasonic transducer having to be attached to a transducer holder using the housing flange, and for this purpose, the housing flange of the transducer housing has to be clamped between a holder flange of the transducer holder and an opposing flange using retraining screws and lock nuts.
2. Description of Related Art
Measurement, control and automation engineering are of special importance in industry. This applies especially to measurement engineering which is the basis for control and automation engineering. One important area of measurement engineering is flow rate measurement engineering (see, the comprehensive treatment of Prof. Dr. sc. nat. Otto Fiedler “Flow and Flow Rate Measurement Engineering”, R. Oldenbourg Verlag Munich 101992). Flow rate measurement according to mechanical action principles, especially variable-area flow meters and Coriolis flow meters, thermal flow meters, magnetic-inductive flow meters and ultrasonic flow meters are of special importance for flow rate measurement engineering (see, “Flow and Flow Rate Measurement Engineering”, op. cit).
Ultrasonic flow meters use the effect that the transport velocity of a medium transported in a measurement tube is superimposed on the propagation velocity of the acoustic signal. The measured propagation velocity of the acoustic signal relative to the measurement tube is therefore greater than in a quiescent medium when the medium is being transported in the direction of the acoustic signal, and the velocity of the acoustic signal relative to the measurement tube is smaller than in the quiescent medium when the medium is being transported opposite the direction of the acoustic signal. The propagation time of the acoustic signal between the acoustic sender and the acoustic receiver—acoustic senders and acoustic receivers are ultrasonic transducers—based on the entrainment effect, is dependent on the transport velocity of the medium relative to the measurement tube, and thus, relative to the ultrasonic transducer, therefore relative to the acoustic sender and the acoustic receiver.
Otherwise, in the prior art underlying the invention, the ultrasonic transducer must be attached to a transducer holder using its housing flange. To do this, the housing flange is clamped between a holder flange of the transducer holder and an opposing flange, using retraining screws and lock nuts.
In particular, when the medium whose flow rate is to be measured has a high temperature, but mainly is under a high pressure, the attachment of the ultrasonic transducer to the transducer holder must meet high demands, in particular it must also be pressure-tight. As FIG. 1 shows, the opposing flange cannot be prevented from arching when the restraining screws are tightened, and as FIG. 1 likewise shows, the arching of the opposing flange likewise leads to an arching of the housing flange of the transducer housing. This is associated with a particular stressing of the housing flange of the transducer housing, but also a particular stress on the gasket which is located between the housing flange of the transducer housing and the holder flange of the transducer holder.